Removed manifest manager refresh + server improvements (#835)

* manifest: removed explicit refresh

Instead, content manager is exposing a revision counter that changes
on each mutation or index change. Manifest manager will be invalidated
whenever this is encountered.

* server: refactored initialization API

* server: added unit tests for repository server APIs (HTTP and REST)

* server: ensure we don't upload contents that already exist

This saves bandwidth, since the client can compute hash locally
and ask the server whether the object exists before starting the upload.

cli/command_server_start.go

@@ -18,7 +18,6 @@
 	"github.com/pkg/errors"
 	prom "github.com/prometheus/client_golang/prometheus"
 	htpasswd "github.com/tg123/go-htpasswd"
-	"google.golang.org/grpc"
 
 	"github.com/kopia/kopia/internal/auth"
 	"github.com/kopia/kopia/internal/clock"
@@ -110,26 +109,11 @@ func runServer(ctx context.Context, rep repo.Repository) error {
 	var handler http.Handler = mux
 
 	if *serverStartGRPC {
-		grpcServer := grpc.NewServer(
-			grpc.MaxSendMsgSize(repo.MaxGRPCMessageSize),
-			grpc.MaxRecvMsgSize(repo.MaxGRPCMessageSize),
-		)
-		srv.RegisterGRPCHandlers(grpcServer)
-
-		log(ctx).Debugf("starting GRPC/HTTP server...")
-
-		httpServer.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			if r.ProtoMajor == 2 && strings.Contains(r.Header.Get("Content-Type"), "application/grpc") {
-				grpcServer.ServeHTTP(w, r)
-			} else {
-				handler.ServeHTTP(w, r)
-			}
-		})
-	} else {
-		log(ctx).Debugf("starting HTTP-only server...")
-		httpServer.Handler = handler
+		handler = srv.GRPCRouterHandler(handler)
 	}
 
+	httpServer.Handler = handler
+
 	if *serverStartShutdownWhenStdinClosed {
 		log(ctx).Infof("Server will close when stdin is closed...")